1. Field of the Invention
The present invention relates generally to devices for preventing a trailer from jackknifing with respect to a tractor and, more particularly, to an anti-jackknife device which is automatically actuated when the brakes of the tractor are applied.
2. Description of the Prior Art
A jackknife is a known condition wherein a trailer follows a tractor in such a way that the longitudinal axis of trailer is oriented with respect to the longitudinal axis of the tractor at an angle of 90 degrees or more. The jackknife condition is often caused to occur when brakes are applied to both the tractor and the trailer, but the effective braking action of the trailer is less than that of the tractor. As a result, the unbraked momentum of the trailer causes the trailer to push up against the tractor causing the rear of the tractor to swing out with respect to the front of the tractor. When a resulting angle is formed between the longitudinal axis of the tractor and the longitudinal axis of the trailer that is 90 degrees or less, the jackknife condition occurs. The jackknife condition is a seriously dangerous condition for a number of reasons. The tractor and trailer move laterally out of theft normal lane path. The driver of the tractor loses control of the tractor and trailer. The tractor and trailer have an increased tendency to flip over.
Throughout the years, a number of innovations have been developed relating to anti-jackknife devices, and the following U.S. Pat. Nos. are representative of some of those innovations: 3,420,547; 3,430,986; 3,774,941; 4,991,863; and Des. 323,804. More specifically, U.S. Pat. No. 3,420,547 discloses an anti-jackknife device that employs hydraulically operated retractable rods that keep the trailer in a straight-line condition with respect to the tractor. A significant disadvantage with the anti-jackknife device is that the straight-line condition is too restrictive for normal operation of a tractor and trailer. Often roads curve, and the straight-line condition may be too restrictive for successfully following a curve in the road without disabling the system. In this respect, it would be desirable if an anti-jackknife device were provided which did not maintain a tractor and trailer in a straight-line orientation.
U.S. Pat. No. 3,430,986 discloses an anti-jackknife device which includes hydraulically operated brake shoes and a clutch plate for preventing relative rotation between the tractor and the trailer. The hydraulically operated brakes shoes are carried entirely by the trailer, and the clutch plate is on the tractor. Two significant disadvantages are associated with this device. First, effective anti-jackknife operation between the brake shoes and the clutch plate depend upon a high coefficient of friction between the two surfaces. Such a high coefficient of friction may be rapidly diminished in the presence of grease from the fifth wheel and in the presence of water from rain or snow. In this respect, it would be desirable if an anti-jackknife device were provided which does not depend upon a high coefficient of friction between two braking surfaces for proper operation.
A second disadvantage with the anti-jackknife device in U.S. Pat. No. 3,430,986 is the fact that much of the device is carried by the trailer as opposed to the tractor. The number of trailers in use is far more numerous than the number of tractors. As a result, many trailer remain idle while tractors are very much utilized. It seems to be an overly expensive proposition to equip trailers with so much of the anti-jackknife device. In this respect, it would be desirable if an anti-jackknife device were provided which were mostly carried by the tractor as opposed to the trailer.
U.S. Pat. No. 3,774,941 discloses an anti-jackknife device which operates with a conventional fifth wheel on the tractor and operates with a conventional tractor having a kingpin which fits into the fifth wheel. A plurality of hydraulically operated locking arms are operated by hydraulic brakes which are automatically operated by the tractor brake system when the tractor brake system is actuated. The locking arms engage recesses in the underside of the trailer. A disadvantage associated with this device is the use of the lever arms and the complementary recesses. The recesses are discrete receptacles for the ends of the locking arms. Consequently, the ends of the locking arms on the tractor and the recesses in the trailer must be placed in discrete registration with each other for the ends of the locking arms to engage the discrete recesses. For this to occur, when the brakes of the tractor are applied, the tractor and the trailer must be in a specific alignment. In actual practice, however, the required specific alignment between the tractor mid the trailer may not be present when the brakes of the tractor are applied and the anti-jackknife locking arms are actuated. The tractor and trailer may be going around a curve in the road when the brakes are applied. If such is the case, the locking arms on the tractor may not engage the recesses on the trailer. In this respect, it would be desirable if an anti-jackknife device were provided which does not depend upon a specific alignment between a tractor and a trailer to be present when the brakes are applied. Also, in this regard, it would be desirable if an anti-jackknife device were provided which is operable when the tractor and trailer are riding on a curve in the road.
U.S. Pat. No. 4,991,863 discloses an anti-jackknife device that employs a retractable latch block employed on the tractor and a plurality of stop blocks employed on the trailer. There are a left stop block and a fight stop block. When a jackknife is about to occur to the left, then one stop block will function, and the other will remain unused. Similarly, when a jackknife is about to occur to the right, then one stop block will function, and the other will remain unused. Each stop block serves to prevent a jackknife in only one direction. For a number of reasons, it would be desirable to spread anti-jackknife forces to more than none stopping device. Safety often demands redundancy, and such redundancy is not present with the device disclosed in U.S. Pat. No. 4,991,863. In this respect, it would be desirable if an anti-jackknife device were provided which spreads anti-jackknifing forces to both a right side and a left side in a redundant manner whether the jackknife is occurring to the right side or the left side.
U.S. Pat. No. Des. 323,804 may also be of interest for its disclosure of an ornamental design for an anti-jackknife device.
Still other features would be desirable in an anti-jackknife apparatus for tractor and trailer connections. For example, there are occasions when brakes may be applied by a driver, and the orientation between the tractor and the trailer is 90 degrees or less. Such conditions often occur when the tractor and trailer are being maneuvered to a loading dock. In this respect, it would be desirable if an anti-jackknife device were provided which can be bypassed when the tractor and trailer are being maneuvered to a loading area.
In addition, the enabling or the disabling of the anti-jackknife apparatus for tractor to trailer connections should be easily accomplished by the tractor driver with the mere actuation of an electrical switch.
Thus, while the foregoing body of prior art indicates it to be well known to use anti-jackknife devices for tractors and trailers, the prior art described above does not teach or suggest an anti-jackknife apparatus for tractor to trailer connections which has the following combination of desirable features: (1) does not maintain a tractor and trailer in a straight-line orientation; (2) does not depend upon a high coefficient of friction between two braking surfaces for proper operation; (3) is mostly carried by the tractor as opposed to the trailer; (4) does not depend upon a specific alignment between a tractor and a trailer to be present when the brakes are applied; (5) is operable when the tractor and trailer are riding on a curve in the road; (6) spreads anti-jackknifing forces to both a right side and a left side in a redundant manner whether the jackknife would occur to the tight side or the left side; (7) can be bypassed when the tractor and trailer are being maneuvered to a loading area; and (8) enabling or disabling the anti-jackknife apparatus is easily accomplished by the tractor driver with the mere actuation of an electrical switch. The foregoing desired characteristics are provided by the unique anti-jackknife apparatus for tractor to trailer connections of the present invention as will be made apparent from the following description thereof. Other advantages of the present invention over the prior art also will be rendered evident.